Method and Device for Applying a Material to a Moving Web

ABSTRACT

In a method for applying a substance to a moving web ( 4 ) of a product, an air-vapor mixture is supplied to at least one nozzle ( 13 ) in which the substance is propelled by means of the air-vapor mixture as propellant in an application zone ( 32 ) on the web ( 4 ) is applied. Excess air-vapor mixture and excess material are removed from the application zone ( 32 ). In order to improve the energy efficiency of such a process, it is proposed that at least part of the excess air-steam mixture discharged from the application zone ( 32 ) be recycled and returned to at least one nozzle ( 13 ). In addition, a device ( 1 ) for carrying out the method described above is proposed.

INTRODUCTION

The invention relates to a method for applying a substance to a moving web of a product, wherein an air-vapor mixture is supplied to at least one nozzle, with which the substance applied by means of the air-vapor mixture as a blowing agent in a deposition zone on the web with excess air-vapor mixture and excess material being removed from the application zone.

Moreover, the invention relates to a device for applying a substance to a moving web of a product, wherein an air-vapor mixture is supplied via a first line at least one nozzle, which is arranged in an enclosure which limits an application zone. Said substance can be applied by means of the air-vapor mixture as a blowing agent on the web and excess air-vapor mixture and excess substance from the application zone can be discharged through a second line.

STATE OF THE ART

The method described at the beginning and the associated apparatus are used in particular in the production of endless webs of fibrous materials, in particular paper or similar nonwovens. The substance with which the web of the material is sprayed, in particular, coated, may be, for example, a paint, a starch, a binder, an adhesive, an impregnating agent or the like. The application of the coating material is typically carried out with a plurality of nozzles, which are arranged transversely to the direction of the web of the material to be coated,

The air-vapor mixture, which is introduced as a propellant through the nozzles in the interior of the enclosure in the application zone, is sucked in the prior art by means of exhaust blown from this housing again. By means of a heat exchanger, the heat energy contained in this exhaust air stream is at least partially withdrawn and used again as process heat for other purposes. Nevertheless, the exhaust air leaving the heat exchanger still contains a comparatively high energy content, so that the delivery of this exhaust air flow to the environment leads to a not inconsiderable loss of energy of the entire system. In addition, it is not possible in all systems or applications, the exhaust air flow over a heat exchanger or use the exhaust air flow in the heat exchanger withdrawn heat otherwise useful.

Task

The invention has for its object to propose a method and apparatus for applying a substance to a moving web of a good, in which or the energy consumption compared to the prior art is reduced,

Solution

Based on a method of the type described above, the underlying object is achieved in that at least a portion of the discharged from the application zone, excess air-steam mixture is recycled and at least one nozzle is fed back.

With the method according to the invention, therefore, not only the heat is withdrawn from the air-vapor mixture, but there is also genuine material recycling, in the sense that the same air-vapor mixture is circulated and thus returned to at least one Duse arrives. In the prior art, as a rule, as much heat as possible is withdrawn from the air-steam mixture, although the dew point may well have fallen below this point and condensate can accumulate. Nevertheless, the system continuously loses energy and water with the volume flow delivered,

On the other hand, in the process according to the invention, the enthalpy of the water contained in the recycled part of the mixture is obtained at least in the part of the air-vapor mixture which is recycled. According to the invention, this energy is thus no longer lost according to the invention, so that significantly less energy has to be used overall than in the prior art.

According to a preferred embodiment of the invention, it is proposed that the air-vapor mixture is dehumidified in the course of recycling, preferably by means of a cyclone and/or a mist eliminator. A cyclone is preferably arranged immediately after the discharge of the air-vapor mixture from the application zone in order to achieve a separation of condensate and to prevent carryover of water into the further line system and beyond at least one conveyor, in the circulation arranged to demand the air-vapor mixture to protect against excessive water pollution. If there is a mist eliminator in the stream of recycled air-steam mixture, the latter can subsequently be supplied to a conveyor, which is very sensitive in terms of water in liquid form such as a rotary compressor.

The invention further configuration is proposed that a portion of the excess air-vapor mixture, preferably after its dehumidification, preferably by means of a cyclone, discharged from the circulation and preferably discharged to the environment. In this way, the volumetric flow rate of the recycled air-steam mixture is reduced in comparison with the volumetric flow supplied to at least one nozzle in the application zone, so that it is possible to obtain a steam admixture to be carried out in the course of recycling (around the temperature and to increase the moisture content of the air-vapor mixture to be supplied to at least one nozzle back to the desired value) without increasing the total mass flow above the required level.

A development of the invention provides that after the removal of a portion of the excess air-steam mixture from the circulation air, preferably Outside air, the recycled stream of air-steam mixture is supplied. In this way, on the one hand, the total volume flow required for the subsequent supply to at least one nozzle is achieved and, on the other hand, it is supplied by the low moisture content (outdoor) created the opportunity to realize the increase in temperature by steam admixture in a later process step, without exceeding the required water content.

In the course of the discharge of a portion of the excess air-vapor mixture and its replacement by supplying air with low moisture content, it is particularly useful from an energetic point of view, that at least a portion of the heat energy of the removed from the circuit part of the excess air-steam mixture is preferably transferred to the air supplied to the circuit to the supplied outside air.

This is preferably done with a heat exchanger.

Before the recycled stream of the air-vapor mixture can be returned to at least one nozzle, it is necessary to increase the temperature to between about 80° C. and about 110° C., including the recycled or air mixed with low moisture recycled stream steam at a temperature between 105° C. and 180° C. and a pressure between 1.2 bar (abs.) and 10 bar (abs.) is added. In the case of strongly superheated steam, steam cooling by means of condensate injection is necessary in order to keep the temperature and humidity within the required limits.

In device-technical terms, the underlying object is achieved by a third line through which a part of the discharged from the second line excess air-vapor mixture in the first conduit is feasible. The formerly open system with material completely separate feed side and discharge side of the air vapor mixture is closed in this way, at least for a partial volume flow of the high-velocity air-vapor mixture. The third line thus forms a connection between the feed side and the discharge side of the housing or application zone.

Preferably, the device according to the invention has a sixth line, through which steam from a steam source into the recycled air-steam mixture is feasible, more preferably, the sixth line is disposed downstream of the junction of the third line in the first line.

The device further configuration is provided that the top-shot air-vapor mixture by means of a process air fan, preferably by means of a side-channel blower, is sucked out of the application zone limiting housing, preferably the side channel blower downstream of a cyclone for separating water from the extracted, excess air-steam mixture is arranged.

In addition, it makes sense to compress the recycled part of the air-steam mixture by means of a rotary compressor, wherein the rotary compressor is preferably arranged before the junction sixth line in the first line. By means of a rotary compressor, the pressure required on the supply side by at least one nozzle can be achieved efficiently.

According to a further embodiment, it is proposed that in the flow direction, after the confluence of the third line in the first line, a mist eliminator and further preferably before the rotary compressor is arranged to a filter, The sensitive to liquid water rotary compressor is protected safely in this way.

The energy efficiency of the device according to the invention is increased when the heat of the discharged to the environment non-recycled part of the excess air-vapor mixture, which is guided in the fifth line, on air through a fourth line and the first line in the direction of at least one nozzle is guided, is transmitted.

EMBODIMENT

The method according to the invention will be explained in more detail below with reference to an exemplary embodiment of a device for its implementation, which is illustrated in the drawing figure. The drawing figure shows a schematic process diagram which explains the procedure according to the invention.

A device 1 for applying a substance, namely a starch suspension, to a moving web 4 of a product, namely a paper web, has an enclosure 2 which, together with a web 4 moving in the direction of an arrow 3, defines an interior space 5. In the upper part of the drawing figure are both guide rollers. 6 as well as the web 4 of the paper and the housing 2 and an applicator 7 are shown in a cross-section, The housing 2 has a cuboid shape and extends over the entire width of the web 4 of the paper extending perpendicular to the plane of the drawing. Two longitudinal sides 8 and a narrow side 9 of the enclosure 2 form together a U, which is closed at an open side of the passing web 4 of the paper, so that a rectangle is formed in cross-section. The end faces of the housing 2 which are not visible in the drawing figure are also closed, so that the interior 5 of the housing 2, except for gap areas 10 between the paper-side ends of the longitudinal sides 8 and the web 4 of the paper, are hermetically closed.

Within the cuboid housing 2 is also the cuboid application device 7, which extends transversely to the direction of the web 4 of the paper above the entire web width. The application device 7 comprises a cuboidal housing 11, to the web 4 of the paper facing top 12 a plurality of vanes arranged in series behind one another 13 is arranged. The nozzles 13 are two-substance nozzles, to each of which a first line 14, an air-steam mixture, and above a further line 15, a starch suspension is fed, Serving as propellant air-vapor mixture is homogeneously mixed in the nozzles 13 with the starch suspension and sprayed uniformly on the facing top of the passing web 4 of the paper. The individual lines 14 for supplying in each case a nozzle 13 with air-steam mixture are supplied by a common manifold 16, which is led out of the housing 2 and connected to an air-steam mixture supply. Similarly, the individual lines 15 are connected to the power supply to a common starch manifold, not shown, which leads to a reservoir 33 for the starch suspension. To that

Reservoir 33 also performs a return line 34 for excess starch suspension, which drains from a sump area of the housing 2.

Via a second line 17, the excess air-vapor mixture from the interior 5 of the housing 2 is removed. The air-vapor mixture also contains a proportion of excess starch suspension and that of less than 1%, The temperature of the air-vapor mixture exiting the interior 5 of the enclosure 2, i.e. when entering the second line 17 is about 70 to 100° C., the relative humidity is about 80 to 100%.

The excess air-vapor mixture then passes into a cyclone 18, and is deposited in the water droplets. The air-steam mixture flows after the cyclone 18 through a process air fan 19, with which the required negative pressure for suction from the housing 2 is generated. When the air-vapor mixture from the process air fan 19 exits, it has a relative humidity of 80% to 100% and a temperature between 70° C. and 100° C.

At a branch 20, a partial volume flow of the air-steam mixture is then discharged via a fifth line 21. The proportion of this volume flow to the total volume flow in the second conduit 17 is about 15 to 20%. The other part of the air-steam mixture is fed via a third line 22 in the circulation. Not in the Circuit-guided, the fifth line 21 flowing part of the air-steam mixture passes before being discharged to the environment a heat exchanger 23, which is also integrated in a fourth line 24 and withdrawn by means of which the exhaust air flowing through the fifth line 21 their heat and fresh air, preferably outside air flowing in the fourth conduit 24, is transferred. At a junction 25, the current flowing through the fourth line 24 and the current flowing through the third line 22 combine with each other. After this junction 25, the relative humidity of the partially recycled and partially “rejuvenated” air-vapor mixture is about 85% to 100% and the temperature about 70° C. to 80° C. This mixing volume flow is now in one first line 26, which extends to the housing 2 located in the application device 7. The above-described mixing volume flow arrives at the passage of a mist eliminator 27 and a filter 28 into a rotary compressor 29. The relative humidity falls after the rotary compressor 29, since the temperature rises very high by the compression heat. At a further junction 30, the third line 26 and a sixth line 31 meet, being supplied by the latter pure steam at a temperature of 105%, i.e. a pressure of 1.2 bar (abs), from a steam generator or steam tank. By means of live steam and optionally condensate injection into a mixing chamber 35, the temperature of the created mixing volume flow behind junction 30 in the third conduit 26 is increased to about 95%. In this state, the partially recycled “fresh” air-vapor mixture mixed with preheated outside air and fresh live steam enters the collection tube 16 of the applicator and then mixes in the nozzles 13 with starch and is sprayed onto the web 4 of the paper.

LIST OF REFERENCE NUMBERS

1 contraption

2 housing

3 arrow

4 web

5 Interior

6 guide roller

7 applicator

8 long side

9 narrow side

10 gap region

11 casing

12 top

13 jet

14 line

15 line

16 manifold

17 second line

18 cyclone

19 Side-channel blower

20 branch

21 fifth line

22 third line

23 heat exchangers

24 fourth line

25 junction

26 first line

27 Droplet

28 filter

29 Rotary compressor

30 junction

31 sixth iine

32 application zone

33 reservoir

24 Return line

35 mixing chamber 

What is claimed is: 1-11. (canceled)
 12. A method for applying a substance to a moving web, the method comprising: supplying an air-vapor mixture to at least one nozzle; applying the substance through the at least one nozzle to the web in an application zone by the air-vapor mixture acting as a propellant; discharging excess air-vapor mixture and excess substance from the application zone; and recycling at least a first portion of the excess air-vapor mixture from the application zone and feeding the first portion of the excess air-vapor mixture back to the at least one nozzle.
 13. The method according to claim 12, further comprising: dehumidifying the first portion of the air-vapor mixture through a cyclone or a mist eliminator during recycling.
 14. The method according to claim 12, further comprising: dehumidifying a second portion of the excess air-vapor mixture through the cyclone; and discharging the second portion of the excess air-vapor mixture downstream of the cyclone into an ambient.
 15. The method according to claim 14, further comprising: adding ambient air to the first portion of the excess air vapor mixture after discharging the second portion of the excess air-vapor mixture downstream of the cyclone into an ambient.
 16. The method according to claim 15, further comprising: transferring heat energy from the second portion of the excess air-vapor mixture to the ambient air added to the first portion of the air vapor mixture downstream of the cyclone.
 17. An apparatus for applying a substance to a moving web, the apparatus comprising: a first conduit that feeds an air-vapor mixture to at least one nozzle arranged in an enclosure that envelops an application zone; a propellant that is formed by the air-vapor mixture and applies the substance to the web in the application zone; a second conduit that discharges excess air-vapor mixture and excess substance from the application zone; a third conduit that feeds a first portion of the excess air-vapor mixture into the first conduit.
 18. The apparatus according to claim 17, further comprising: a fourth conduit through which steam from a vapor source is introduced into the first portion of the excess air-vapor mixture, wherein the fourth conduit is arranged at the first conduit downstream of a junction of the third conduit and the first conduit.
 19. Apparatus according to claim 17, wherein the excess air-vapor mixture is vacuum extracted by a side channel blower from the enclosure that envelops the application zone, and wherein the side channel blower is arranged downstream of a cyclone that separates water from the excess air-vapor mixture.
 20. The apparatus according to claim 17, further comprising: a rotary compressor that compresses the first portion of the excess air-vapor mixture and that is arranged in the first conduit upstream of a junction of the first conduit and a sixth conduit.
 21. The apparatus according to claim 20, further comprising: a mist eliminator that is arranged in the first conduit downstream of a junction of the third conduit and the first conduit; and a filter that is arranged in the first conduit downstream of the mist eliminator and upstream of the rotary compressor.
 22. The apparatus according to claim 14, further comprising: a heat exchanger that extracts heat from a second portion of the excess air-vapor mixture, exhausts the second portion of the excess air vapor mixture into an ambient, wherein the heat exchanger transfers the heat to ambient air that is fed through a fourth conduit and the first conduit to the at least one nozzle. 